1. Field of the Invention
The present invention relates to an electronic seal for a container or compartment. More particularly, it relates to a seal having a sealing strip and a monitoring device. When the monitoring device senses that the seal has been broken, it records information regarding the break in memory, which can be retrieved later.
2. The Prior Art
Seals according to the prior art are used on the locks of cargo compartments, ships' holds, crates or containers. These seals can detect whether or not a secured lock has been opened during transportation. One type of known seal includes a sealing wire and a lead seal connecting the ends of the wire. This seal has the disadvantage that an opened lock can easily be manipulated to simulate an undamaged seal. Another disadvantage is that in the case of an authorized opening of the seal, another lead seal has to be used since they are not re-usable.
U.S. Pat. No. 4,766,419 discloses an electronic seal which avoids these two disadvantages associated with a lead seal. A random number generator, including a clock generator and a counter, is activated by opening the seal. Such activation produces a new number combination, which is displayed. In order to be able to produce the preceding number combination, it may be necessary to open and close the seal innumerable times, which would largely exclude the aforementioned tampering. As in the case of authorized opening, the new number combination is indicated in the forwarding papers, thus obviating the need to replace the seal following each opening.
However, this seal only provides information as to whether or not the secured lock may have been opened. The time and frequency of the seal break is not apparent. However, such information could clarify the question as to whether a break was intentional, improper or accidental.